The purpose of this project is to show that various changes which are common in currently developing countries may result in higher marital fertility than was observed earlier. 1) Rose Frisch's work shows that there is a negative relationship between the percentages of a female's body weight which is fat and the frequency of anovulatory cycles. It is hypothesized that in an actual population this mechanism operates primarily through overall caloric consumption rather than in response to the nutritional balance or protein content of the diet. 2) Based on work on Ireland and Soviet Central Asia, it is hypothesized that men over age forty-five are substantially less fecund than younger mature men. In many developing countries, the marriage pattern is changing from one with a large age difference between spouses to a smaller difference. This should result in increased marital fertility. 3) Throughout sub-Saharan Africa there are tribal differences in intercourse taboos during lactation. A breakdown in taboos, perhaps due to partial substitution of animal milk for mother's milk along with the effect of the animal milk supplements in shortening postpartum amenorrhea would also result in higher marital fertility. These hypotheses will be tested using data from socio-demographic and socio-economic surveys of cities in Zaire, in which birth control was not practiced to any significant extent. With households as units, the exogenous effects of nutrition and age of spouses on fertility can be examined. Data on animal milk consumption along with tribal differences in taboos can be used to separate their effects on fertility. The frequency of proposals for reducing fertility through increases in female age of marriage, along with desires to improve nutrition and the observed trend in substitution of animal for mother's milk, make these issues of vital importance in currently developing countries.